package ${basePackage}.core.hutool.io.watch.watchers;

import ${basePackage}.core.hutool.collection.ConcurrentHashSet;
import ${basePackage}.core.hutool.io.watch.Watcher;
import ${basePackage}.core.hutool.util.ThreadUtil;

import java.nio.file.Path;
import java.nio.file.Paths;
import java.nio.file.WatchEvent;
import java.nio.file.WatchService;
import java.util.Set;

/**
 * 延迟观察者<br>
 * 使用此观察者通过定义一定的延迟时间，解决{@link WatchService}多个modify的问题<br>
 * 在监听目录或文件时，如果这个文件有修改操作，会多次触发modify方法。<br>
 * 此类通过维护一个Set将短时间内相同文件多次modify的事件合并处理触发，从而避免以上问题。
 *
 * @author Looly
 * @since 3.1.0
 */
public class DelayWatcher implements Watcher {

    /**
     * Path集合。此集合用于去重在指定delay内多次触发的文件Path
     */
    private final Set<Path> eventSet = new ConcurrentHashSet<>();
    /**
     * 实际处理
     */
    private final Watcher watcher;
    /**
     * 延迟，单位毫秒
     */
    private final long delay;

    //---------------------------------------------------------------------------------------------------------- Constructor start

    /**
     * 构造
     *
     * @param watcher 实际处理触发事件的监视器{@link Watcher}，不可以是{@link DelayWatcher}
     * @param delay   延迟时间，单位毫秒
     */
    public DelayWatcher(Watcher watcher, long delay) {
        //Assert.notNull(watcher);
        if (watcher instanceof DelayWatcher) {
            throw new IllegalArgumentException("Watcher must not be a DelayWatcher");
        }
        this.watcher = watcher;
        this.delay = delay;
    }
    //---------------------------------------------------------------------------------------------------------- Constructor end

    @Override
    public void onModify(WatchEvent<?> event, Path currentPath) {
        if (this.delay < 1) {
            this.watcher.onModify(event, currentPath);
        } else {
            onDelayModify(event, currentPath);
        }
    }

    @Override
    public void onCreate(WatchEvent<?> event, Path currentPath) {
        watcher.onCreate(event, currentPath);
    }

    @Override
    public void onDelete(WatchEvent<?> event, Path currentPath) {
        watcher.onDelete(event, currentPath);
    }

    @Override
    public void onOverflow(WatchEvent<?> event, Path currentPath) {
        watcher.onOverflow(event, currentPath);
    }

    //---------------------------------------------------------------------------------------------------------- Private method start

    /**
     * 触发延迟修改
     *
     * @param event       事件
     * @param currentPath 事件发生的当前Path路径
     */
    private void onDelayModify(WatchEvent<?> event, Path currentPath) {
        Path eventPath = Paths.get(currentPath.toString(), event.context().toString());
        if (eventSet.contains(eventPath)) {
            //此事件已经被触发过，后续事件忽略，等待统一处理。
            return;
        }

        //事件第一次触发，此时标记事件，并启动处理线程延迟处理，处理结束后会删除标记
        eventSet.add(eventPath);
        startHandleModifyThread(event, currentPath);
    }

    /**
     * 开启处理线程
     *
     * @param event       事件
     * @param currentPath 事件发生的当前Path路径
     */
    private void startHandleModifyThread(final WatchEvent<?> event, final Path currentPath) {
        ThreadUtil.execute(new Runnable() {
            @Override
            public void run() {
                ThreadUtil.sleep(delay);
                eventSet.remove(Paths.get(currentPath.toString(), event.context().toString()));
                watcher.onModify(event, currentPath);
            }
        });
    }
    //---------------------------------------------------------------------------------------------------------- Private method end
}
